Best fit and 1σ error region that we obtain by fitting the CAK-type mass-loss prescription as described in Bestenlehner (2020, red solid line and shaded area) to our observed mass-loss rates (blue circles, dark and light error bars denote 1σ and 2σ uncertainties). The best fit values we derive are shown in the bottom right corner. For comparison we show the CAK-type prescription also for the case of α_eff = 0.50, as obtained by fitting the slope of the modified wind momentum (dark red dashed line). Eight sources that lie close or above Γ_e,trans are labelled with their abbreviated identifications (e.g. a1 is R136a1).